If it is really grainy there isn't a heck of a lot you can do. If not too bad try color curves and/or cranking up the contrast and turning down the brightness, that will minimize the 'noise' in the very dark scenes about as good as anything. If you're using version four also try the gain adjustment with the offset in combination with gamma and also play around with the older levels filter.

I once had a very poor scene almost total darkeness that with a lot of trial and error at least got to look half way decent. It least you could see some detail. Also a pinch of blur may help.

You could get the filter the Satish wrote for Vegas that allows use of Virtual Dub filters and then get the some variant of Donald Graft's "Smart Smoother" Virtual Dub plugin. You can find Donald Graft's filter at:

http://shelob.mordor.net/dgraft/

I don't have the URL to the Satish "adapter" handy. You can probably find it by searching the forum.

John